1. Field of the Invention
This invention relates to an air conditioner for an automobile, and more particularly, it is concerned with a control device for such air conditioner for an automobile, which closes one of two coaxial cylinders in a rolling piston type capacity-changeable compressor to reduce the cooling capability of the air conditioner and to eliminate waste input into the compressor when the passenger cabin in the automobile has attained a desired temperature, thereby providing constantly a comfortably air-conditioned passenger cabin.
2. Description of Prior Art
Generally speaking, the control device for the automobile cooling device carries out the temperature control within the passenger cabin of the automobile by turning on and off of an electromagnetic clutch which is equipped on the compressor and transmits driving force of an automobile engine through detection of a temperature of an outlet air which has passed through a cooling device in the passenger cabin or a temperature of an inlet air into the cooling device, and through comparison of the detected temperature with a preset cabin temperature.
In such temperature control method, however, when the cabin temperature is approaching a preset temperature level, there tends to occur such a phenomenon that the abovementioned electromagnetic clutch begins to turn on and off frequently to maintain the cabin temperature at the predetermined level, thereby continuing and discontinuing the operations of the compressor. When the compressor runs into this condition, the temperature of the outlet air which has passed through the cooling device undergoes abrupt change due to the continued and discontinued operations of the compressor by the turn-on and off of the compressor, on account of which the occupants in the passenger cabin feel uncomfortableness owing to their directly receiving cooled air within the cabin. Further, even when high and low pressure conditions in the cooling cycle take a balance with a cooling load after stoppage of operations of the compressor due to turning off of the electromagnetic clutch, and the electromagnetic clutch turns on again as the result of the balancing, there is inevitable waste in input until the cooling cycle reaches its high and low pressure levels to enable it to perform the required work.